1. Related Applications
This application is a US National Stage Application pursuant to 35 USC xc2xa7371 based on the International Application PCT/EP99/02112, filed Mar. 25, 1999, which in turn claims the priority of the German Application DE 198 13 165.8, filed Mar. 25, 1998.
2. Field of the Invention
The invention relates to a method and a device for the cutting machining of non-circular internal and external contours, for example cam profiles.
Known methods of this type use a conical grinding wheel that is carried by a spindle positioned at a certain angle in relation to the workpiece. This procedure has the advantage that, in particular for long workpieces such as camshafts, the grinding spindle can be constructed with a short, and thus rigid, design. If a grinding wheel in the shape of the cone or truncated cone is used, it must, however, be ensured that the surface line of the grinding surface on the wheel that engages with the workpiece is parallel to the desired surface; otherwise, the desired surface cannot be created, and a distortion of the surface occurs instead.
It is not a problem for dynamically balanced (circular) surfaces to be ground because the grinding wheel must only be aligned accordingly in relation to the workpiece. But for dynamically unbalanced (non-circular) surfaces, this is not possible with a stationary alignment of the grinding wheel in relation to the workpiece.
DE 196 20 813 A1 and WO 97/44159 therefore introduce a method for grinding cams in which the truncated cone-shaped grinding wheel is moved up and down on a Y axis in relation to the workpiece in order to ensure a corresponding alignment in relation to the workpiece. In this respect, reference is made to FIG. 4 of these documents.
When machining the displayed cam, a stationary alignment of the grinding wheel according to the unbroken line would cause the grinding zone on the grinding wheel to be shifted between points A and B due to the non-circular cam contour. Since the surface line of the grinding surface at the points above and below the axis, that is, also on points A and B, is not parallel to the desired surface, an unwanted distortion of the ground surface would occur in this area.
To prevent this distortion, the mentioned documents provide that the grinding wheel is moved along the Y axis, for example into the position indicated by the broken lines. Although this does prevent a distortion, it was found that for certain contours no satisfactory grinding result can be obtained in this manner.
The invention is based on the task of creating a method, as well as a device for the cutting machining of non-circular internal and external contours, which ensures a high machining quality.
This objective is realized by the characteristics of Claims 1 and 2, or 13 and 14 respectively.
The invention is based on the idea of realizing this objective with a continuous relative movement between tool and workpiece and achieving a satisfactory machining result. In the process, the inventors found that an optimum result can be obtained with a swivel movement, since this swiveling of the tool or workpiece results in a wobbling (or sweeping) movement, which again results in a high quality machining result, since no machining marks are created. Furthermore, in certain machining tasks, substantially better machine dynamics and a more favorable acceleration of the tool in relation to the workpiece can be achieved in this manner.
The invention creates a method for the cutting machining of non-circular contours, such as cams, which uses a tool in the shape of a cone or a truncated cone, for example a grinding wheel, positioned on a spindle for rotation, with said spindle aligned at a certain angle with the workpiece axis on which the workpiece with the contour is positioned, whereby the tool is swiveled during the machining about at least one first swivel axis that is different from the spindle axis.
Since, naturally, the crucial factor here is solely the relative movement between tool and workpiece, the workpiece can be moved accordingly as an alternative. For this purpose, the tool is swiveled during the machining about at least one first swivel axis that is different from the workpiece axis.
Preferably, the first swivel axis is arranged parallel to the spindle axis or workpiece axis at a certain distance. In addition, good machining results can be obtained if the tool or workpiece is swiveled during machining also about a second swivel axis. Here also, the crucial factor is solely the relative movement between tool and workpiece, so that it is also possible to swivel the tool about one axis, and the workpiece about another axis (sequentially or simultaneously).
In principle, very different orientations of the swivel axes are conceivable to achieve the desired effect and to keep the engagement line of the tool parallel to the desired surface. An orientation of the first swivel axis vertical to the spindle axis or the workpiece axis was found to be successful, whereby the second swivel axis stands vertical to the spindle axis or workpiece axis and also still vertical to the first swivel axis.
The first swivel axis is preferably located in the area of the tool or the contour to be machined. Furthermore, it was found that a successful arrangement of the second swivel axis is located on the spindle axis behind the first swivel axis when seen from the workpiece (10xe2x80x2 in FIG. 2).
To increase the machining possibilities, the tool may be positioned so that it can slide along the spindle axis, for example in a linear bearing. To adjust the machine to the actual machining task or to the particular tool used, for example to the cone angle of a conical grinding wheel, the angle of the spindle axis may be adjustable in relation to the workpiece axis.
It was also found to be advantageous if the workpiece can be machined with at least two tools while it is mounted. This means that while grinding a camshaft, a pre-grinding with a grinding disk that has a relatively large diameter is possible, for example, which is then followed by a final grinding with a grinding wheel that has a smaller diameter. For this purpose, the spindle head for positioning the spindle can be swiveled to permit the engagement of another tool positioned on the spindle head with the workpiece.
For camshafts, for example, angled or crowned contours of the cams may be desirable. To achieve them, the tool may be provided with such a surface line. If necessary, the tool, as one example, a grinding wheel, can be adjusted accordingly. The invention is explained below in more detail in reference to two exemplary embodiments.